Valve trains of the pre-cited type are sufficiently well-known in the technical field and need no further detailed description here. An internal exhaust gas recirculation within narrow limits takes place due to valve overlap. For example, the quantity of exhaust gas returned to the combustion chamber by the exhaust gas system is determined by the point of time of closing of the exhaust valve. This can lead to advantages with regard to consumption and emission. Besides this, a late point of time of closing of the exhaust valve reduces the induction work because less throttling is required for load regulation.
It can be said, in general, that the quantities of exhaust gas recirculated due to design-related valve overlaps in engines without a variable valve control are relatively small.
The technical world is further familiar with solutions in which an external exhaust gas recirculation is used. In this case, exhaust gas components are extracted at the exhaust manifold and returned to the intake manifold through complex pipe systems. In addition to the pipes, it is also necessary to provide return valves for the exhaust gas in these solutions.